1. Field of the Invention
This invention relates to a dielectric material. More particularly, it relates to a dielectric material which is obtained by sintering while suppressing reduction reaction in the inside thereof and therefore exhibits stable dielectric characteristics. The dielectric material of the present invention has excellent dielectric characteristics, i.e., a relatively high relative dielectric constant (hereinafter represented by .di-elect cons..sub.r), a small absolute value of the temperature coefficient of resonance frequency (hereinafter resonance frequency is represented by f.sub.o, and the temperature coefficient thereof is represented by .tau..sub.f), and a large value of unloaded quality coefficient (hereinafter represented by Q.sub.u). The dielectric material of the present invention is suited for use in multilayer circuit boards, resonators and filters particularly for use in a high frequency region, an impedance matching element for various microwave circuits, and the like.
2. Description of the Related Art
With the recent increase of communication information, rapid progress is being made in various communication systems utilizing the microwave region, such as mobile telecommunication systems, satellite communication systems, positioning systems using communication data, and satellite broadcasting. Many microwave dielectric materials have been developed accordingly. Microwave dielectric materials for these uses are required to have (1) a high relative dielectric constant .di-elect cons..sub.r, (2) a small absolute value of the temperature coefficient .tau..sub.f of resonance frequency f.sub.o (i.e., small temperature dependence of f.sub.o), and (3) a large unloaded quality coefficient Q.sub.u (i.e., a small dielectric loss 1/Q.sub.u).
Ba(Mg.sub.1/3 Ta.sub.2/3) O.sub.3 and Ba(Zn.sub.1/3 Ta.sub.2/3) O.sub.3 are known to be dielectric materials having a small dielectric loss, i.e., a large Q.sub.u. In Japanese Patent 2736439 is disclosed a dielectric porcelain composition based on BaO--Nd.sub.2 O.sub.3 --Sm.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 having incorporated therein an Mn oxide. Additionally, a dielectric porcelain composition containing an Mn compound and having a high dielectric constant is disclosed in JP-B-61-17083 and Japanese Patent 2840673.
However, depending on the components contained, cases sometimes occur with these known dielectric materials, in which the inside of the material (sintered body) is in a reduced state due to shortage of oxygen during sintering, failing to exhibit stable dielectric characteristics. This is particularly observed with large sintered bodies such as those used in large-sized resonators.